1. Field of the Invention
This invention relates to a rotary drum assembly for forming an agglomerated product from agglomerative materials and more particularly to a rotary scraper that is supported within a first drum member of a pair of longitudinally aligned drum members to control the thickness and configuration of the layer of agglomerative materials deposited on the inner wall of the first drum member to aid in the mixing and agglomeration of the agglomerative materials.
2. Description of the Prior Art
In the process of distilling coal and forming coke, as described in U.S. Pat. Nos. 3,073,315; 3,401,089 and 3,562,783, particulate bituminous coal and finely divided char (the solid carbonaceous residue of coal which has been distilled at a temperature of between 800.degree. and 1400.degree. F.) is introduced into a rotary drum. Depending on the type of coal employed and the ratio of coal to char, pitch may also be added as a binder. The preheated coal and char supply substantially all the heat required to achieve the desired elevated temperature necessary to agglomerate the carbonaceous materials.
The materials are intimately mixed by rotation of the drum. As the constituents are mixed, the coal particles are further heated to such an extent that partial distillation of the coal particles occurs, evolving tar and forming a loosely coherent, plastic sticky mass in the rotary drum. Rotation of the drum mixes the loosely coherent, plastic mass and forms fine plastic particles which grow in size as a result of the tumbling action of the plastic mass of particulate material in the drum. During the mixing or ball forming stage, the rate of flow of the agglomerative materials through the drum, the rotational speed of the drum and the inclination of the drum relative to the horizontal frame are factors in determining the size of the agglomerated product.
Growth of the plastic particles is attained by a snowballing type of tumbling or rolling action on the upper inclined exposed surface of the plastic mass of particulate material in the drum. Repeated tumbling or rolling of the particles causes the continued growth of the plastic particles into agglomerates. The agglomerates will continue to grow until the binder evolved by the coal particles and the pitch binder, if employed, loses its plasticity. Thereafter, the agglomerates in the drum rigidify or harden to form uniformly sized particles that are discharged from the outlet portion of the drum. It is desirable that the agglomerated product formed be uniformly sized, perferably in the range of between 3/4 to 2 inches. Agglomerates having a size greater than about 2 inches and less than about 3/4 inches are considered unacceptable for use in a conventional blast furnace or other conventional metallurgical processes.
Rotation of the drum deposits a layer of the finely divided agglomerative material on the inner surface of the drum. As illustrated in U.S. Pat. No. 3,348,260, a fixed scraper controls the thickness of the layer for coating of the agglomerative materials deposited on the surface of the drum. U.S. Pat. Nos. 2,697,068 and 3,316,585 disclose a rotary scraper positioned within a single rotary drum and operable to continuously remove agglomerative materials from the inner wall of the drum so that a uniform thickness is maintained on the wall of the drum. The rearward end portion of the scraper shaft is supported within the drum. The support arrangement requires a large tubular portion and a spider arrangement located within the drum. The size of the rotary scraper limits the maximum diameter of the drum member. Thus, a drum having a relatively large diameter requires a longer torque arm and consequently a greater moment is applied to the torque arm.
As illustrated in U.S. Pat. Nos. 2,778,056; 2,695,221 and 1,921,114; British Pat. No. 779,302; Canadian Pat. No. 627,037 and East German Pat. No. 740,613, a single rotary drum includes a rotary scraper for maintaining a layer of agglomerative material of a preselected thickness on the wall of the drum. The scrapers disclosed extend the length of the drums with the scraper shaft end portions supported externally of the rotary drum. As a result, the end portions of the scraper shaft extending through the end portions of the rotary drum must be sealed to prevent the escape of gas and material from the drum end portions and maintain a preselected pressure within the drum, if required.
Additional problems are encountered with supporting the end portions of a rotary scraper within a rotary drum. Specifically, the bearing support for the scraper provides no resistance for the scraping action. The scraper has a tendency to twist out of the way of the agglomerative materials to substantially decrease the effectiveness of the rotary scraper. In addition, because the temperature within the drum member exceeds 850.degree. F., a cooling lubricant must be supplied to the scraper bearing assembly. With the bearing positioned within the drum, the fluid must be pumped through the center tubular portion of the scraper from the feed end through the drum to the discharge end and back. Consequently, the tubular body portion of the scraper must be insulated to insure that the lubricant is sufficiently cool when it reaches the bearing to provide the necessary lubrication.
There is need for a rotary drum assembly in the forming of an agglomerated product from agglomerative materials in which the rotary scraper thereof extends the length of the product forming stage and is rotatably supported within the drum to permit unrestricted relative rotation between the scraper assembly and the rotary drum and is efficiently supplied with coolant fluid to maintain the temperature of the scraper bearings below a preselected temperature.